Spray painting apparatus



Dec. 19, 1961 Filed Nov. 5, 1958 H. F. BOK ETAL 3,013,730

SPRAY PAINTING APPARATUS 4 Sheets-Sheet l INVENTOR flH/DR/K F 50K EDWARD 50K BY M ATTORNEY De 1 1 6 H. F. BOK ET AL 3,013,730

SPRAY PAINTING APPARATUS Filed Nov. 5, 1958 4 Sheets-Sheet 2 INVENTOR HENDR/K F 50K EDWARD 50K ATTORNEY 1961 H. F. BOK ET AL 3,013,730

SPRAY PAINTING APPARATUS Filed Nov. 5, 1958 4 Sheets-Sheet 3 I 54 l d8 :20 62 J v Q JO 2 5/ 1 J 47 48 7 I I II INVENTOR HE/VD/Q/K F 50% L DWAPD 50K BY M ATTORNEY Dec. 19, 1961 H. F. BOK ETAL SPRAY PAINTING APPARATUS 4 Sheets-Sheet 4 Filed Nov. 5, 1958 INVENTOR f/E/VDR/K F 50K EDWARD 50K BY 10/2 ATTORNEY 3,013,730 Patented Dec. 19, 1961 iands Filed Nov. 5, 1958, Ser. No. 772,084 8 (Iiairns. (Cl. 239-125) The invention relates to a spray painting apparatus, wherein the pressure medium is produced by the evaporation of a volatile liquid, such as a hydrocarbon, and is fed from an evaporating chamber to a spray gun.

A spray painting apparatus of this kind has been disclosed in our U.S. Patent Numbers 2,790,063 and 2,840,681.

During the operation of such a spray painting apparatus, the developed vapor may recondense when the temperature of the hose is too low; this phenomenon will occur in particular during the start of the paint spraying operation, and upon restarting this operation after an interruption.

As this condensation strongly interferes with the required formation of a dry pressure medium, it has already een proposed to restrict the condensation by providing a heating element within the hose. However, in that case, the hose has to meet very special requirements, and its flexibility is unfavorably afi'ected.

it is an object of the present invention to provide a spray painting apparatus wherein the pressure medium will always leave the spray nozzle in a dry condition without the necessity of using a heating element within the hose.

it is a further obiect of the invention to provide a simple manner of preheating the spray gun in order to prevent a condensation of the vapor within the spray gun.

It is still a further object of the present invention to facilitate the manipulation of the spray gun.

It is another object of the invention to provide a spray painting apparatus which yields a dry spraying medium even if the spraying operation is repeatedly interrupted.

According to a main feature of the invention, the supply conduit leading the pressure medium from the evaporating chamber to the spray nozzle is provided with a branch conduit which is connected with a condensing device.

In this manner, it is possible to obtain a vapor flow through the hose when the spray gun is shut off; this vapor flow heats the hose and is then led to the condensing device.

Preferably, the branch conduit is provided with a shut off valve, so that the vapor flow to the condensing device may be closed down as soon as the hose has been sufiiciently heated to enable the vapor to pass without condensation; after that, the spray gun may be operated in the usual manner. Y in a preferred embodiment of the invention, a detachable connection is provided between the branch conduit and the condensing device.

Furthermore, it may be convenient to locate the connection between the branch conduit and the supply conduit within the spray gun, so that the vapor also passes through a part of the spray gun before reaching the branch conduit. In this manner, it is made possible to preheat the paint in the paint supply conduit within the spray gun to such an extent that the temperature and the viscosity of this paint at the start of the spraying operation have the same values as during a continued spraying operation.

In a preferred embodiment of the spray painting apparatus according to the invention, a flow limiter is provided in the branch conduit leading to the condensing device. This makes it possible to maintain a connection between the condensing device and the supply conduit during the spray painting operation, so that a limited vapor flow (f.i. 15% of the total flow) is led to the condensing device when the spray gun is in operation. In the case of spray painting operations which are repeatedly interrupted, this continuous vapor fiow through the branch conduit prevents a condensation of the vapor in the hose or in the spray gun without the necessity of switching on the condensing device at each interruption.

Preferably, the passage opening of the flow limiter is adjustable, so that a large passage opening may be used during the initial preheating period, and a small passage opening during the actual spraying period.

Thus, only a short initial preheating period of the spray painting apparatus is necessary, even when a flow limiter is used.

As the quantity of liquid which condenses in the condensing device may be rather considerable and may even amount to 50% of the total amount of evaporated liquid it may be advantageous to connect the condensing device with the evaporating device and to insert a pump in this connection, which returns the condensed liquid to the evaporating device. The pump may feed the liquid either continuously or discontinuously to the evaporating device, against the pressure prevailing therein.

The invention will be more fully described with reference to the accompanying drawings which show various embodiments of the spray painting apparatus according to the invention. 7

FIG. 1 is a schematic longitudinal sectional View of a spray painting apparatus, according to the invention provided with a condensing device which operates discontinuously.

FIG. 2 is a schematic longitudinal sectional view of a modification of the spray painting apparatus according to FIG. 1, wherein the condensing device operates continuously.

FIG. 3 is a sectional view of a spray gun to be used in the apparatus according to FIGS. 1 and 2.

FIG. 4 shows a detail of the return conduit leading from the condensing device to the evaporator.

FIG. 5 is a schematic longitudinal sectional View of a spray painting apparatus with continuous liquid supply, provided with a continuously operating condensing device.

FIG. 6 is a schematic longitudinal sectional view of a modification of the spray painting apparatus according to FIG. 5, wherein a dilferent circulation system has been used.

' FIG. 7 is a schematic longitudinal view of a spray painting apparatus according to the invention. wherein the condensing device has been shown in detail.

FIGURE 8 is a schematic sectional view of a modiiication of the spray painting apparatus according to FIGURE 2 wherein the pump is connected to the main supply tank. V FIG. 1. shows a spray painting installation, provided with an evaporating device 1 for converting a volatile liquid, such as petroleum, ether, into a vapor under pressure which is used as a spraying medium for the paint and which is fed via vapor outlet 57 and attached vapor circuit 5% to the spray gun 6 through a hose 4, provided with a shut off valve 5. The evaporating device 1 comprises an evaporating chamber 3, in which an electric heating element 2 is mounted for the evaporation of the liquid, and a liquid supply vessel 7 which is connected to the evaporating chamber 3 by means of a first passage opening 8 and a second passage opening 9. The opening 8 lies below the liquid level in the liquid supply vessel 7, and is dimensioned in such manner that the maximumliquid supply to the evaporating chamber cor responds approximately with the evaporating capacity of the heating element. The second opening 9 is provided in the upper part of the separating wall between the evaporating chamber 3 and the liquid supply vessel 7 and lies above the liquid level in the supply vessel 7 and in the evaporating chamber 3. The opening 9 may be closed by means of a valve 1%, which is actuated by a float 14 through an actuating rod 13 and a lever 11, said lever being pivotally connected to the wall 12 of the evaporating chamber 3.

in order to prevent condensation in the hose and to preheat the spray gun 6, in particular during the initial preheating period of the spraying operation, the spray gun 6 is provided with a discharge 15 which may be shut oil by means of a shut off valve 16 and which may be coupled with a coupling tube 17 of a condensing device 13; the coupling tube 17 is provided with a valve 19.

During the initial heating period of the apparatus, the spray nozzle is shut oil and the developed vapor, which is still wet, is discharged into the condensing device 18, in which it is cooled and caused to condense. In this manner, both the hose 4 and the spray gun 6 are preheated without any loss of spraying liquid through the spray nozzle.

The discharge of the mixture of vapor and condensate to the condensing device 18 is continued until the hose and the spray gun 6 are heated to such a temperature, that no condensation of the vapor flowing from the evaporator 1 through the hose 4 and through the spray gun 6 will occur anymore.

Thereupon the discharge of a dry invisible vapor for use as a pressure medium for the paint may be eiiected through the spray nozzle of the spray gun 6, whilst the discharge conduit 15 may be disconnected from the coupling tube 17 after the valves 16 and 19 have been closed.

The liquid in the condensing device 18 may be fed into a main supply tank for the spraying liquid through a conduit 2i), which is provided with a valve 21.

The liquid supply vessel 7 may be refilled periodically through the filling device 22, through which liquid from the main supply tank is poured, f.i. by means of a funnel.

FIG. 2 shows a modified embodiment of the evaporating device 1, comprising a superheating cap 23, whilst an annular pressure equalising channel is formed between the superheating cap 23 and the envelope 24.

When the operation of a spray painting apparatus with an unheated hose 4 is frequently interrupted, a large amount (f.i. 50%) of the liquid which is fed into the liquid supply vessel 7 will finally be collected in the condensing device 18, which will have to be switched on at each interruption.

For this reason, the spray painting apparatus according to FIG. 2 is constructed in such manner that the spraying liquid collected in the condensing device is not fed to a main supply tank, but directly to the liquid supply vessel 7.

For this purpose, the hose 4 is connected with the spray gun 6 as well as with a return conduit 28 by means of a three way block 26. The three way block 26 is connected with the spray gun 6 by means of a conduit 27. A flow limiter 29, which may be adjustable, is arranged between the hose 28 and the condensing device 18.

The discharge of the condensing device 18 is connected with the liquid supply vessel 7 through a conduit 32, comprising a pump 30 driven by a motor 31, and a shut off valve 33.

When the evaporating device 1 is in operation and the spray gun is shut off, the vapor flows through the fiow limiter 29 to the condensing device 18 and condenses therein. The liquid and the vapor which may still be present in the condensing device are pumped through the conduit 32 and the open valve 33 into the liquid supply vessel 7.

In a modified embodiment, the flow limiter 29 may be located between the three way block 26 and the return conduit 28, or be included in the three way block 26, or in the return conduit inside the spray gun 6.

When the spray gun 6 is opened, the gas flow through the return hose 28 continues, as the return hose 28 remains in open connection with the evaporating device. The pump 30 is continuously driven, whilst the shut off valves 5 and 33 are normally opened and are only closed, if a break down occurs in the circulation system, or it the spray gun has to be disconnected.

A modified embodiment of the spray painting installa tion according to the invention is shown in FIG. 8; in this embodiment, the filling device 22 may be dispensed with.

In this modified embodiment, the suction side of the continuously driven pump 39 is also connected to the main supply tank 36 through the conduit 34 which is provided with a shut olf valve 35.

The shut oti valve 35 is normally closed, in which case no liquid is fed from the main supply tank 36 to the liquid supply vessel 7.

Ir" the liquid level in the liquid supply vessel 7 has decreased to such an extent that a refill is necessary, the shut oil valve 35 is opened, whereafter the pump 30 feeds liquid from the condensing device 18 as well as from the main supply tank 36 into the liquid supply vessel 7. By means of a liquid meter (not shown) indicating the liquid level in the liquid supply vessel 7, the filling operation may be observed, so that the shut off valve 35 may be closed after the liquid supply vessel 7 has been refilled.

Thereafter, the circulation through the condensing device may be restarted, and the spraying operations may be continued after a short preheating period.

FIG. 3 schematically shows an embodiment of the spray gun 6 which may be used in the above described spray painting installation.

The supply hose 4 for the pressure medium is connected with the spray gun 6 by means of a connecting part 37. The vapor flows through the connecting part 37, the channel 38 and the channel 39 into the chamber 40 and when the shut off pin 41 is brought into its open position, the vapor may escape through the channey 42 and the spray head 43.

The channel 38 is connected with the return hose 23 through the channels 44 and 45 and the connecting part 46.

The vapor flows continuously from the hose 4 to the return hose 28 during the discharge of the pressure medium through the spray head 43 as well as during any interruption thereof, so that the spriy gun 6 is continuously heated.

If the paint spraying operation is resumed after an interruption, a dry pressure medium is immediately available; in addition, the paint sprayed in the initial period has obtained an increased temperature, as this paint has filled the paint supply conduits in the front part of the spray gun 6 during the interruption, and has been preheated due to the heat transfer in the spray gun.

According to FIG. 2, the return conduit 28 for the pressure medium is fixedly secured to the three way block 26; as an alternative, this connection may be detachable, so that the return hose 28 may be disconnected during the spraying operations as well as during short interruptions, whereby the spray gun 6 is much easier to handle.

FIG. 4 shows such a detachable connection between the three way block 26 and the return hose 28.

During the preheating period, the coupling parts 15 and 17 are interconnected and the shut off valves 16 and 17 are opened either automatically or manually, so that the circulation system through the return hose 28 comes into operation.

During the spraying operations, the coupling may be disconnected and the valves 16 and 19 may be closed, so that the circulation system is rendered inoperative. During interruptions of the spraying operation, the coupling parts may be interconnected again in order to prevent the hose 4 and the spray gun 6 from being cooled.

FIG. 5 shows another modification of the spray painting apparatus, wherein the evaporation device 1 consists of an evaporating chamber 3, to which the liquid to be evaporated is fed from a main supply tank 36, whilst a pump 30 is fitted in the connecting conduit 34 between the supply tank 36 and the evaporating chamber 3. The debouchrnent 47 of the delivery conduit 32 in the evaporating chamber 3 may be wholly or partly closed by means of a valve 48 which is actuated by a float 14 within core 49.

The pump 30 is continuously driven by a motor 31. The delivery conduit 32 connecting the pump 36 to the evaporation chamber 3 is connected with the suction conduit between the pump 34 and the supply tank 36 by means of a bypass conduit 50 which is provided with a pressure regulating valve 51.

A return conduit 28 connects the spray gun 6 with the condensing device 18, which is further connected with the suction side of the pump 30.

if the spray gun 6 is closed and the valve 5 is opened, the circulation system is in operation, and the hose 4 as well as the spray gun 6 are heated.

The discharge conduit 34 ofthe main supply tank 36 i provided with a shut oil valve 52, which is normally opened and which is only closed when the spray painting apparatus is out of use. 1

FIG. 6 shows a simplified embodiment of the circulation system according to FIG. 5, wherein a return conduit 53 from the pump 3% to the liquid tank 36 is used as a condensing device and further replaces the by-pass conduit St A portion (ii. 20%) of the liquid supplied by the pump is continuously fed to the evaporating chamber 3, whilst the remainder of the vapor f.i. 80% returns to the supply tank through the conduit 53.

In this embodiment the large quantity of liquid flowing through the circulation system is used for condensing the vapor which returns from the spray gun 6 through the conduit 28; for this purpose, the return conduit 23 debouches into the conduit 53. As the quantity of vapor flowing through the return conduit 28 per unit of time constitutes in its condensed condition only a small portion (f.i. 515%) of the total amount of circulating liquid flowing through the conduit 53, this vapor will completely condense in the conduit 53, so that this conduit acts as a condensing device and makes the use of a separate condensing unit superfluous. The return conduit 53 debouches into the lower part of the main supply tank 35.

FIG. 7 shows a spray painting apparatus substantially corresponding with the appartus according to FIG. 2. The condensing device 18 has been shown in section. The return flow of vapor from the spray gun 6 through the return conduit passes through the condensing conduit 54, which is surrounded by the liquid in the condensing device and which enters into the condensing device 18 through a flaring outlet 55, which is provided with holes 56. Preferably, the condensing device is partly filled with water on which the condensed liquid floats whilst the liquid spraying medium is removed from the upper part of the condensing device 18 through the conduit 20.

It will be understood that the condensing device may be constructed in any other suitable manner, f.i. as a surface condenser.

In paint spraying apparatus wherein the paint is fed to the spray gun by means of a hose, the paint may be heated by means of a heat transfer from the return hose for the spraying medium to the paint conduit. For this purpose, the hoses may be positioned adjacent to each other, or the paint hose may be placed within the return hose for the vapor.

Various alterations may be made in the constructive details of the several forms of spray painting apparatus disclosed hereinbefore, without departing from the scope of the invention.

What we claim is:

1. A spray painting apparatus, comprising a pressure tank adapted to contain a volatile liquid; a heating element mounted in said tank and contacting said volatile liquid; means defining an inlet for the liquid in the tank; means defining a vapor outlet in the tank; a main vapor circuit, including a conduit connected with said vapor outlet in said tank, a spray gun connected with said conduit and a spray nozzle incorporated in said spray gun; a branch conduit leading from said main vapor circuit between said vapor outlet and said spray nozzle so as to receive vapor prior to its discharge through said nozzle, a condensing device connected with said branch conduit and conduit means interconnecting said condensing device and said pressure tank.

2. A spray painting apparatus, comprising a pressure tank adapted to contain a volatile liquid; a heating element mounted in said tank; means defining an inlet for the liquid in the tank; means defining a vapor outlet in the tank; a main vapor circuit, including a conduit connected with said vapor outlet in said tank, a spray gun connected with said conduit and a spray nozzle incorporated in said spray gun; a branch conduit connected with said main vapor circuit between said vapor outlet and said spray nozzle, a shut ofi valve inserted in said branch conduit, a condensing device connected with said branch conduit behind said shut ofl valve and coupling means inserted in said branch conduit between said shut off valve and said condensing device.

3. A spray painting apparatus, comprising a pressure tank adapted to contain a volatile liquid; a heating element mounted in said tank; means defining an inlet for the liquid in the tank; means defining a vapor outlet in the tank; a main vapor circuit, including a conduit connected with said vapor outlet in said tank, a spray gun connected with said conduit and a spray nozzle incorporated in said spray gun; a branch conduit connected with said main vapor circuit between said vapor outlet and said spray nozzle; a shut off valve inserted in said branch conduit, a flow limiter inserted in said branch conduit and a condensing device connected with said branch conduit behind said shut off valve and said flow limiter.

4. A spray painting apparatus, comprising a pressure tank adapted to contain a volatile liquid; a heating element mounted in said tank; means defining an inlet for the liquid in the tank; means defining a vapor outlet in the tank; a main vapor circuit, including a flexible conduit connected with said vapor outlet in said tank, a spray gun connected with said flexible conduit and a spray nozzle incorporated in said spray gun; a branch conduit connected with said main vapor circuit between said vapor outlet and said spray nozzle; a condensing device connected with said branch conduit; a return conduit connected with said condensing device and with said pressure tank and pump means inserted in said return conduit.

5. A spray painting apparatus, comprising a pressure tank adapted to contain a volatile liquid; a heating element mounted in said tank; means defining an inlet for the liquid in the tank; means defining a vapor outlet in the tank; a main vapor circuit, including a flexible conduit connected with said vapor outlet in said tank; a spray gun connected with said flexible conduit and a spray nozzle incorporated in said spray gun; a branch conduit connected with said main vapor circuit between said vapor outlet and said spray nozzle; a shut oif valve inserted in said branch conduit; an adjustable flow limiter inserted in said branch conduit; a condensing device connected with said branch conduit behind said shut off valve and said flow limiter, a return conduit connected with said condensing device and with said 0 pressure tank and pump means inserted in said return conduit.

6. A spray painting apparatus, comprising a pressure tank adapted to contain a volatile liquid; a heating element mounted in said tank; means defining an inlet for the liquid in the tank; means defining a vapor outlet in the tank; a main vapor circuit, including a flexible conduit connected with said vapor outlet in said tank; a spray gun connected with said flexible conduit and a spray nozzle incorporated in said spray gun; a branch conduit connected with said main vapor circuit between said vapor outlet and said spray nozzle; a condensing device connected with said branch conduit; a return conduit connected with said condensing device and with said pressure tank and pump means inserted in said return conduit; a branch conduit connected with the return conduit between the pump means and the condensing device and a main liquid supply tank connected with said last mentioned branch conduit.

7. A spray painting apparatus, comprising a pressure tank adapted to contain a volatile liquid; a heating element mounted in said tank; means defining an inlet for the liquid in the tank; a supply conduit connected with said inlet; a main liquid supply tank connected with said supply conduit; pump means inserted in said supply conduit; a by-pass conduit connecting the pressure and the suction side of the said pump means; a pressure regulating valve inserted in said by-pass conduit; means defining a vapor outlet in said tank; a main vapor circuit, including a flexible conduit connected with said vapor outlet in said tank, a spray gun connected with said flexible conduit and a spray nozzle incorporated in said spray gun; a branch conduit connected with said main vapor circuit between said vapor outlet and said spray nozzle; a condensing device connected with said branch conduit and a return conduit connected with said condensing device and with the suction side of said pump means.

8. A spray painting apparatus, comprising a pressure tank adapted to contain a volatile liquid; a heating element mounted in said tank; means defining an inlet for the liquid in the tank; a supply conduit connected with said inlet; a main liquid supply tank connected with said supply conduit; pump means inserted in said supply conduit; a by-pass conduit connecting the pressure side of the pump means with the said main liquid supply tank, a pressure regulating valve inserted in said by-pass conduit, means defining a vapor outlet in said tank; a main vapor circuit including a flexible conduit connected with said vapor outlet in said tank, a spray gun connected with said flexible conduit and a spray nozzle incorporated in said spray gun; a branch conduit connected with said main vapor circuit between said vapor outlet and said spray nozzle and further connected with the by-pass conduit between the pressure regulating valve and the main liquid supply tank.

References Cited in the file of this patent UNITED STATES PATENTS 2,016,407 Wentzel Oct. 8, 1935 2,036,446 Tsutsuni Apr. 7, 1936 2,083,611 Marshall June 15, 1937 2,199,454 Andler May 7, 1940 2,292,946 Karig Aug. 11, 1942 ,565,543 Arvintz et al. Aug. 28, 1951 

